A tower such as a wind turbine tower must be secured to a foundation in some way. In the case of a concrete foundation, for example, the lower section of a wind turbine tower is usually anchored to the foundation using anchor bolts that were previously embedded in the concrete. The “heads” of the anchor bolts are usually fixed in steel anchor plates that were laid horizontally in the foundation and covered with a suitably thick layer of concrete, so that most of each anchor bolt is embedded and only a relatively short section of each anchor bolt remains protruding vertically upward from the surface of the foundation.
However, it is very difficult to achieve a perfectly horizontal upper surface of foundation. At the same time, it is necessary to ensure that a lower tower section is placed horizontally, otherwise the resulting unbalanced loading would stress the tower structure and may lead to irreparable damage. In some known approaches, a horizontal alignment is achieved by first estimating where a height adjustment might be necessary, placing shims over the appropriate anchor bolt ends, and repeating the process until the corrections are deemed sufficient. The tower flange of the lowest tower section can then be lowered into place over the “corrected” anchor bolt ends. If the correction was performed properly, the lower surface of the tower flange will lie in the desired horizontal plane. However, such a procedure is very time-consuming, since great effort must be invested to determine what corrections are necessary and whether the corrections are sufficient before putting the lowest tower section into place.
In another approach, a leveling ring can be used as an intermediate layer between the foundation and the tower flange. Such a leveling ring is arranged to fit over the anchor bolts, and grout is pushed under the leveling ring in various places until an upper surface of the leveling ring is essentially horizontal. Once the grout has hardened, the bottom tower section is lowered into place over the anchor bolts and these are secured. However, this approach is also difficult to get right, since it is not easy to achieve a perfectly horizontal alignment of the leveling ring. This is because a tower can have a very large lower diameter, depending on the generating capacity of the wind turbine, and a leveling ring must be at least as wide. The diameter at the tower base can be in the range of 3.0 to 6.0 meters, for example about 4.0 meters for a 3 Megawatt wind turbine. Since a leveling ring must also be made of a strong material such as steel, it is a very heavy component and therefore difficult to manipulate, particularly when a very precise leveling adjustment must be made in the millimeter range. Thus a need exists to provide an improved way of providing a horizontal mounting surface for a wind turbine tower.